StreetDeck Steering Wheel Control

Hello I'm a new user from Norway, I have installed StreetDeck on my carputer in my BMW X5 2002 model. I was wondering if anyone could tell me how to connect my buttons on the steering wheel to control my StreetDeck. I have read a few threads about this, including Chuck's detailed post about a phidget encoder, but I don't seem to understand how I connect the wires from my steering wheel to the computer. Is there any interface wich I can connect the wires from the steering wheel that will convert the signal to USB?